1. Field of the Invention
Embodiments disclosed herein relate to methods and apparatus for treating drilling fluids. More specifically, embodiments disclosed herein relate to methods and apparatus for separating particulate solids and water from an invert emulsion drilling fluid.
2. Background Art
When drilling oil and/or gas wells, oil-based drilling fluids are often used to cool the drill bit, remove rock chips, and control subsurface fluids. After used, this fluid, known as drilling mud, contains undesirable solids. Before the mud can be used again, the solids must be removed.
Various devices are used to remove solids from drilling fluid. Large solids are often removed by passing the fluid through a vibrating porous membrane, or screen, thereby segregating the solids that are too large to pass through the screen. A centrifugal force may be applied to the fluid to remove finer solids from the drilling mud. However, ultra fine solids, i.e., those solids that are not removed from the fluid by mechanical means, such as vibratory separators and centrifuges, remain in the oil-based mud even after such processing. Additionally, continual re-use of the drilling fluid increases the amount of ultra fine solid contaminants present in the fluid.
Ultra fine solids may affect many fluid system properties adversely. Formation clays are unavoidably incorporated into the fluid system, and, depending on their nature and amount, the clay minerals may be beneficial or harmful to the fluid system. Contaminants, such as gypsum, can “cut” the fluid system causing particles to flocculate and the viscosity to increase. When this occurs, there is danger of torquing the drill pipe to the point of breakage or danger of causing a blowout. At high temperatures, gelation or thickening of the fluid may occur, leading to increased pressure on the recirculation pump.
As drilling fluids are used to drill multiple wells, fine low gravity solids (LGS) (i.e., solids less than 5 μm) build up, because they cannot be removed by separation equipment (e.g., shakers, decanting centrifuges, etc.). Traditionally, drilling fluids are diluted to reduce the LGS concentration and reformulated back to the required properties. This is often costly and also increases the volume of drilling fluid, which leads to storage, transportation and disposal issues. In severe cases, the whole volume of mud is disposed and a fresh fluid is mixed, at significant cost. The environmental impact of continuously disposing large volumes of fluid must be addressed and disposal volumes reduced.
In addition to LGS, water and other liquids (liquid chemicals and brine droplets) also become entrained in the drilling fluid, and cannot be removed by standard separation equipment (e.g., shakers, decanting centrifuges, etc.). Traditionally, drilling fluids are diluted to reduce the water concentration of the invert emulsion drilling fluid. For example, oil may be added to the drilling fluid, such that the oil/water ratio is consistent with the desired needs of the invert emulsion fluid for a particular application or drilling operation. This is often costly and also increases the volume of drilling fluid, which leads to storage, transportation and disposal issues.
Accordingly, there exists a need for improved methods and apparatus for invert emulsion drilling fluid recycling. Additionally, there exists a need for improved methods for removing ultra fine solids and water from drilling fluids that increase the effective fluid lifespan and reduce the need for dilution and disposal of the fluid.